Frequency re-use for service and gateway beams

ABSTRACT

A method is presented for communicating data in a multibeam satellite system utilizing frequency re-use. The method comprises establishing uplink service beams and downlink service beams between a satellite and a plurality of subscriber terminals. A plurality of the uplink service beams are transmitted to the satellite by re-using at least one common uplink frequency channel. A plurality of the downlink service beams are transmitted from the satellite by re-using at least one common downlink frequency channel. The method further comprises establishing at least one uplink feeder beam and at least one downlink feeder beam between the satellite and a gateway terminal. The at least one uplink feeder beam is transmitted to the satellite by further re-using the at least one common uplink frequency channel. The at least one downlink feeder beam is transmitted from the satellite by further re-using the at least one common downlink frequency channel.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims priority to U.S. patentapplication Ser. No. 12/406,870, entitled “FREQUENCY RE-USE FOR SERVICEAND GATEWAY BEAMS,” filed Mar. 18, 2009, which is a continuationapplication of International Application No. PCT/US2007/079567, filedSep. 26, 2007, which claims the benefit of priority of the followingU.S. Provisional Applications: U.S. Provisional Application No.60/827,927, filed Oct. 3, 2006; U.S. Provisional Application No.60/827,924, filed Oct. 3, 2006; U.S. Provisional Application No.60/827,959, filed Oct. 3, 2006; U.S. Provisional Application No.60/827,960, filed Oct. 3, 2006; U.S. Provisional Application No.60/827,964, filed Oct. 3, 2006; and U.S. Provisional Application No.60/827,038, filed Sep. 26, 2006. This application expressly incorporatesby reference each of the above applications.

FIELD OF THE INVENTION

The present invention relates to wireless communications in general and,in particular, to a satellite communications network.

BACKGROUND OF THE INVENTION

Consumer broadband satellite services are gaining traction in NorthAmerica with the start up of star network services using Ka bandsatellites. While such first generation satellite systems may providemulti-gigabit per second (Gbps) per satellite overall capacity, thedesign of such systems inherently limits the number of customers thatmay be adequately served. Moreover, the fact that the capacity is splitacross numerous coverage areas further limits the bandwidth to eachsubscriber.

While existing designs have a number of capacity limitations, the demandfor such broadband services continues to grow. The past few years haveseen strong advances in communications and processing technology. Thistechnology, in conjunction with selected innovative system and componentdesign, may be harnessed to produce a novel satellite communicationssystem to address this demand.

SUMMARY OF THE INVENTION

The present invention relates to a method for communicating data in amultibeam satellite system utilizing frequency re-use.

The method comprises establishing service beams including uplink servicebeams and downlink service beams between a satellite and a plurality ofsubscriber terminals, each downlink service beam being associated with adifferent service beam coverage area, to form a plurality of servicebeam coverage areas. A plurality of the uplink service beams aretransmitted to the satellite by re-using at least one common uplinkfrequency channel, and a plurality of the downlink service beams aretransmitted from the satellite by re-using at least one common downlinkfrequency channel.

The method further comprises establishing at least one uplink feederbeam and at least one downlink feeder beam between the satellite and agateway terminal, the at least one downlink feeder beam being associatedwith a feeder beam coverage area separated from the plurality of servicebeam coverage areas, the at least one uplink feeder beam being receivedat the satellite to form a plurality of the downlink service beams, aplurality of the uplink service beams being received at the satellite toform the at least one downlink feeder beam. The at least one uplinkfeeder beam is transmitted to the satellite by further re-using the atleast one common uplink frequency channel, and the at least one downlinkfeeder beam is transmitted from the satellite by further re-using the atleast one common downlink frequency channel.

According to an embodiment of the invention, the at least one uplinkfeeder beam comprises multiple uplink feeder beams, and the at least onedownlink feeder beam comprises multiple downlink feeder beams. Aplurality of the uplink feeder beams are transmitted to the satellite byyet further re-using the at least one common uplink frequency channel.Also, a plurality of the downlink feeder beams are transmitted from thesatellite by yet further re-using the at least one common downlinkfrequency channel.

According to one embodiment, the at least one uplink feeder beamcomprises 4 carriers, wherein the at least one common uplink frequencychannel comprises two frequency channels, each of the two frequencychannels capable of being separated by right hand circular polarization(RHCP) and left hand circular polarization (LHCP), to form 4 uniquecombinations of frequency and polarization, and wherein each of the 4carriers is transmitted using one of the 4 unique combinations offrequency and polarization.

According to one embodiment, the at least one downlink feeder beamcomprises 4 carriers, wherein the at least one common downlink frequencychannel comprises two frequency channels, each of the two frequencychannels capable of being separated by right hand circular polarization(RHCP) and left hand circular polarization (LHCP), to form 4 uniquecombinations of frequency and polarization, and wherein each of the 4carriers is transmitted using one of the 4 unique combinations offrequency and polarization.

According to one embodiment, each uplink service beam comprises 1carrier, wherein the at least one common uplink frequency channelcomprises two frequency channels, each of the two frequency channelscapable of being separated by right hand circular polarization (RHCP)and left hand circular polarization (LHCP), to form 4 uniquecombinations of frequency and polarization, and wherein each carrier ofan uplink service beam is transmitted using one of the 4 uniquecombinations of frequency and polarization.

According to one embodiment, each downlink service beam comprises 1carrier, wherein the at least one common downlink frequency channelcomprises two frequency channels, each of the two frequency channelscapable of being separated by right hand circular polarization (RHCP)and left hand circular polarization (LHCP), to form 4 uniquecombinations of frequency and polarization, and wherein each carrier ofa downlink service beam is transmitted using one of the 4 uniquecombinations of frequency and polarization. The at least one commonuplink frequency channel may include a 500 MHz frequency channel. The atleast one common downlink frequency channel may include a 500 MHzfrequency channel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a block diagram of an exemplary satellite communicationssystem configured according to various embodiments of the invention.

FIG. 1B is a block diagram illustrating an alternative embodiment of asatellite communication system.

FIG. 2A is an example of a multi-beam system configured according tovarious embodiments of the invention are shown.

FIG. 2B is another example of a multi-beam system configured accordingto various embodiments of the invention are shown.

FIG. 3 presents an embodiment of a ground system of gateways shown inblock diagram form.

FIG. 4 presents an embodiment of a SMTS shown in block diagram form.

FIG. 5 presents an embodiment of a satellite shown in block diagramform.

FIG. 6A presents an embodiment of an upstream translator shown in blockdiagram form.

FIG. 6B presents an embodiment of a downstream translator shown as ablock diagram.

FIG. 7 is a block diagram illustrating a set of subscriber equipmentwhich may be located at a subscriber location for the reception andtransmission of communication signals.

FIG. 8 shows an embodiment of a downstream channel.

FIG. 9 shows an embodiment of an upstream channel.

FIG. 10 shows an embodiment of a gateway transmitter.

FIG. 11 shows an embodiment of gateway receiver.

FIG. 12A illustrates an embodiment of a forward link distributionsystem.

FIG. 12B illustrate an embodiment of a return link distribution system.

FIG. 13 shows an embodiment of a channel diagram.

FIG. 14 presents an illustrative frequency re-use plan that may beadopted in accordance with one embodiment of the invention.

FIG. 15 presents an illustrative system employing adaptive use ofsatellite uplink bands in accordance with one embodiment of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

Various embodiments of the present invention comprise systems, methods,devices, and software for a novel broadband satellite network. Thisdescription provides exemplary embodiments only, and is not intended tolimit the scope, applicability or configuration of the invention.Rather, the ensuing description of the embodiments will provide thoseskilled in the art with an enabling description for implementingembodiments of the invention. Various changes may be made in thefunction and arrangement of elements without departing from the spiritand scope of the invention.

Thus, various embodiments may omit, substitute, or add variousprocedures or components as appropriate. For instance, it should beappreciated that in alternative embodiments, the methods may beperformed in an order different than that described, and that varioussteps may be added, omitted or combined. Also, features described withrespect to certain embodiments may be combined in various otherembodiments. Different aspects and elements of the embodiments may becombined in a similar manner. Also, a number of steps may be requiredbefore, after, or concurrently with the following embodiments.

It should also be appreciated that the following systems, methods,devices, and software may be a component of a larger system, whereinother procedures may take precedence over or otherwise modify theirapplication.

FIG. 1A is a block diagram of an exemplary satellite communicationssystem 100 configured according to various embodiments of the invention.The satellite communications system 100 includes a network 120, such asthe Internet, interfaced with a gateway 115 that is configured tocommunicate with one or more subscriber terminals 130, via a satellite105. A gateway 115 is sometimes referred to as a hub or ground station.Subscriber terminals 130 are sometimes called modems, satellite modemsor user terminals. As noted above, although the communications system100 is illustrated as a geostationary satellite 105 based communicationsystem, it should be noted that various embodiments described herein arenot limited to use in geostationary satellite based systems, for examplesome embodiments could be low earth orbit (LEO) satellite based systems.

The network 120 may be any type of network and can include, for example,the Internet, an IP network, an intranet, a wide-area network (“WAN”), alocal-area network (“LAN”), a virtual private network, the PublicSwitched Telephone Network (“PSTN”), and/or any other type of networksupporting data communication between devices described herein, indifferent embodiments. A network 120 may include both wired and wirelessconnections, including optical links. Many other examples are possibleand apparent to those skilled in the art in light of this disclosure. Asillustrated in a number of embodiments, the network may connect thegateway 115 with other gateways (not pictured), which are also incommunication with the satellite 105.

The gateway 115 provides an interface between the network 120 and thesatellite 105. The gateway 115 may be configured to receive data andinformation directed to one or more subscriber terminals 130, and canformat the data and information for delivery to the respectivedestination device via the satellite 105. Similarly, the gateway 115 maybe configured to receive signals from the satellite 105 (e.g., from oneor more subscriber terminals) directed to a destination in the network120, and can format the received signals for transmission along thenetwork 120.

A device (not shown) connected to the network 120 may communicate withone or more subscriber terminals, and through the gateway 115. Data andinformation, for example IP datagrams, may be sent from a device in thenetwork 120 to the gateway 115. The gateway 115 may format a MediumAccess Control (MAC) frame in accordance with a physical layerdefinition for transmission to the satellite 130. A variety of physicallayer transmission modulation and coding techniques may be used withcertain embodiments of the invention, including those defined with theDVB-S2 and WiMAX standards. The link 135 from the gateway 115 to thesatellite 105 may be referred to hereinafter as the downstream uplink135.

The gateway 115 may use an antenna 110 to transmit the signal to thesatellite 105. In one embodiment, the antenna 110 comprises a parabolicreflector with high directivity in the direction of the satellite andlow directivity in other directions. The antenna 110 may comprise avariety of alternative configurations and include operating featuressuch as high isolation between orthogonal polarizations, high efficiencyin the operational frequency bands, and low noise.

In one embodiment, a geostationary satellite 105 is configured toreceive the signals from the location of antenna 110 and within thefrequency band and specific polarization transmitted. The satellite 105may, for example, use a reflector antenna, lens antenna, array antenna,active antenna, or other mechanism known in the art for reception ofsuch signals. The satellite 105 may process the signals received fromthe gateway 115 and forward the signal from the gateway 115 containingthe MAC frame to one or more subscriber terminals 130. In oneembodiment, the satellite 105 operates in a multi-beam mode,transmitting a number of narrow beams each directed at a differentregion of the earth, allowing for frequency re-use. With such amultibeam satellite 105, there may be any number of different signalswitching configurations on the satellite, allowing signals from asingle gateway 115 to be switched between different spot beams. In oneembodiment, the satellite 105 may be configured as a “bent pipe”satellite, wherein the satellite may frequency convert the receivedcarrier signals before retransmitting these signals to theirdestination, but otherwise perform little or no other processing on thecontents of the signals. A variety of physical layer transmissionmodulation and coding techniques may be used by the satellite 105 inaccordance with certain embodiments of the invention, including thosedefined with the DVB-S2 and WiMAX standards. For other embodiments anumber of configurations are possible (e.g., using LEO satellites, orusing a mesh network instead of a star network), as evident to thoseskilled in the art.

The service signals transmitted from the satellite 105 may be receivedby one or more subscriber terminals 130, via the respective subscriberantenna 125. In one embodiment, the antenna 125 and terminal 130together comprise a very small aperture terminal (VSAT), with theantenna 125 measuring approximately 0.6 meters in diameter and havingapproximately 2 watts of power. In other embodiments, a variety of othertypes of antennas 125 may be used at the subscriber terminal 130 toreceive the signal from the satellite 105. The link 150 from thesatellite 105 to the subscriber terminals 130 may be referred tohereinafter as the downstream downlink 150. Each of the subscriberterminals 130 may comprise a single user terminal or, alternatively,comprise a hub or router (not pictured) that is coupled to multiple userterminals. Each subscriber terminal 130 may be connected to consumerpremises equipment (CPE) 160 comprising, for example computers, localarea networks, Internet appliances, wireless networks, etc.

In one embodiment, a Multi-Frequency Time-Division Multiple Access(MF-TDMA) scheme is used for upstream links 140, 145, allowing efficientstreaming of traffic while maintaining flexibility in allocatingcapacity among each of the subscriber terminals 130. In this embodiment,a number of frequency channels are allocated which may be fixed, orwhich may be allocated in a more dynamic fashion. A Time DivisionMultiple Access (TDMA) scheme is also employed in each frequencychannel. In this scheme, each frequency channel may be divided intoseveral timeslots that can be assigned to a connection (i.e., asubscriber terminal 130). In other embodiments, one or more of theupstream links 140, 145 may be configured with other schemes, such asFrequency Division Multiple Access (FDMA), Orthogonal Frequency DivisionMultiple Access (OFDMA), Code Division Multiple Access (CDMA), or anynumber of hybrid or other schemes known in the art.

A subscriber terminal, for example 130-a, may transmit data andinformation to a network 120 destination via the satellite 105. Thesubscriber terminal 130 transmits the signals via the upstream uplink145-a to the satellite 105 using the antenna 125-a. A subscriberterminal 130 may transmit the signals according to a variety of physicallayer transmission modulation and coding techniques, including thosedefined with the DVB-S2 and WiMAX standards. In various embodiments, thephysical layer techniques may be the same for each of the links 135,140, 145, 150, or may be different. The link from the satellite 105 tothe gateway 115 may be referred to hereinafter as the upstream downlink140.

Turning to FIG. 1B, a block diagram is shown illustrating an alternativeembodiment of a satellite communication system 100. This communicationsystem 100 may, for example, comprise the system 100 of FIG. 1A, but isin this instance described with greater particularity. In thisembodiment, the gateway 115 includes a Satellite Modem TerminationSystem (SMTS), which is based at least in part on the Data-Over-CableService Interface Standard (DOCSIS). The SMTS in this embodimentincludes a bank of modulators and demodulators for transmitting signalsto and receiving signals from subscriber terminals 130. The SMTS in thegateway 115 performs the real-time scheduling of the signal trafficthrough the satellite 105, and provides the interfaces for theconnection to the network 120.

In this embodiment, the subscriber terminals 135 use portions ofDOCSIS-based modem circuitry, as well. Therefore, DOCSIS-based resourcemanagement, protocols, and schedulers may be used by the SMTS forefficient provisioning of messages. DOCSIS-based components may bemodified, in various embodiments, to be adapted for use therein. Thus,certain embodiments may utilize certain parts of the DOCSISspecifications, while customizing others.

While a satellite communications system 100 applicable to variousembodiments of the invention is broadly set forth above, a particularembodiment of such a system 100 will now be described. In thisparticular example, approximately 2 gigahertz (GHz) of bandwidth is tobe used, comprising four 500 megahertz (MHz) bands of contiguousspectrum. Employment of dual-circular polarization results in usablefrequency comprising eight 500 MHz non-overlapping bands with 4 GHz oftotal usable bandwidth. This particular embodiment employs a multi-beamsatellite 105 with physical separation between the gateways 115 andsubscriber spot beams, and configured to permit reuse of the frequencyon the various links 135, 140, 145, 150. A single Traveling Wave TubeAmplifier (TWTA) is used for each service link spot beam on thedownstream downlink, and each TWTA is operated at full saturation formaximum efficiency. A single wideband carrier signal, for example usingone of the 500 MHz bands of frequency in its entirety, fills the entirebandwidth of the TWTA, thus allowing a minimum number of space hardwareelements. Spotbeam size and TWTA power may be optimized to achievemaximum flux density on the earth's surface of −118 decibel-watts permeter squared per megahertz (dbW/m²/MHz). Thus, using approximately 2bits per second per hertz (bits/s/Hz), there is approximately 1 Gbps ofavailable bandwidth per spot beam.

With reference to FIG. 12A, an embodiment of a forward link distributionsystem 1200 is shown. The gateway 115 is shown coupled to an antenna110, which generates four downstream signals. A single carrier with 500MHz of spectrum is used for each of the four downstream uplinks 135. Inthis embodiment, a total of two-frequencies and two polarizations allowfour separate downstream uplinks 135 while using only 1 GHz of thespectrum. For example, link A 135-A could be Freq 1U (27.5-28.0 GHz)with left-hand polarization, link B 135-B could be Freq 1U (27.5-28.0)GHz with right-hand polarization, link C could be Freq 2U (29.5-30 GHz)with left-hand polarization, and link D could be Freq 2U (29.5-30 GHz)with left-hand polarization.

The satellite 105 is functionally depicted as four “bent pipe”connections between a feeder and service link. Carrier signals can bechanged through the satellite 105 “bent pipe” connections along with theorientation of polarization. The satellite 105 converts each downstreamuplink 135 signal into a downstream downlink signal 150.

In this embodiment, there are four downstream downlinks 150 that eachprovides a service link for four spot beams 205. The downstream downlink150 may change frequency in the bent pipe as is the case in thisembodiment. For example, downstream uplink A 135-A changes from a firstfrequency (i.e., Freq 1U) to a second frequency (i.e., Freq 1D) throughthe satellite 105. Other embodiments may also change polarizationbetween the uplink and downlink for a given downstream channel. Someembodiments may use the same polarization and/or frequency for both theuplink and downlink for a given downstream channel.

Referring next to FIG. 12B, an embodiment of a return link distributionsystem is shown. This embodiment shows four upstream uplinks 145 fromfour sets of subscriber terminals 125. A “bent pipe” satellite 105 takesthe upstream uplinks 145, optionally changes carrier frequency and/orpolarization (not shown), and then redirects them as upstream downlinks140 to a spot beam for a gateway 115. In this embodiment, the carrierfrequency changes between the uplink 145 and the downlink 140, but thepolarization remains the same. Because the feeder spot beams to thegateway 115 is not in the coverage area of the service beams, the samefrequency pairs may be reused for both service links and feeder links.

Turning to FIGS. 2A and 2B, examples of a multi-beam system 200configured according to various embodiments of the invention are shown.The multi-beam system 200 may, for example, be implemented in thenetwork 100 described in FIGS. 1A and 1B. Shown are the coverage of anumber of feeder and service spot beam regions 225, 205. In thisembodiment, a satellite 215 reuses frequency bands by isolating antennadirectivity to certain regions of a country (e.g., United States, Canadaor Brazil). As shown in FIG. 2A, there is complete geographicexclusivity between the feeder and service spot beams 205, 225. But thatis not the case for FIG. 2B where there may in some instances be servicespot beam overlap (e.g., 205-c, 205-d, 205-e), while there is no overlapin other areas. However, with overlap, there are certain interferenceissues that may inhibit frequency band re-use in the overlappingregions. A four color pattern allows avoiding interference even wherethere is some overlap between neighboring service beams 205.

In this embodiment, the gateway terminals 210 are also shown along withtheir feeder beams 225. As shown in FIG. 2B, the gateway terminals 210may be located in a region covered by a service spotbeam (e.g., thefirst, second and fourth gateways 210-1, 210-2, 210-4). However, agateway may also be located outside of a region covered by a servicespotbeam (e.g., the third gateway 210-3). By locating gateway terminals210 outside of the service spotbeam regions (e.g., the third gateway210-3), geographic separation is achieved to allow for re-use of theallocated frequencies.

There are often spare gateway terminals 210 in a given feeder spot beam225. The spare gateway terminal 210-5 can substitute for the primarygateway terminal 210-4 should the primary gateway terminal 210-4 fail tofunction properly. Additionally, the spare can be used when the primaryis impaired by weather.

Referring next to FIG. 8, an embodiment of a downstream channel 800 isshown. The downstream channel 800 includes a series of superframes 804in succession, where each superframe 804 may have the same size or mayvary in size. This embodiment divides a superframe 804 into a number ofvirtual channels 808(1-n). The virtual channels 808(1-n) in eachsuperframe 804 can be the same size or different sizes. The size of thevirtual channels 808(1-n) can change between different superframes 804.Different coding can be optionally used for the various virtual channels808 (1-n). In some embodiments, the virtual channels are as short as onesymbol in duration.

With reference to FIG. 9, an embodiment of an upstream channel 900 isshown. This embodiment uses MF-TDMA, but other embodiments can use CDMA,OFDM, or other access schemes. The upstream channel 900 has 500 MHz oftotal bandwidth in one embodiment. The total bandwidth is divided into mfrequency sub-channels, which may differ in bandwidth, modulation,coding, etc. and may also vary in time based on system needs.

In this embodiment, each subscriber terminal 130 is given atwo-dimensional (2D) map to use for its upstream traffic. The 2D map hasa number of entries where each indicates a frequency sub-channel 912 andtime segment 908(1-5). For example, one subscriber terminal 130 isallocated sub-channel m 912-m, time segment one 908-1; sub-channel two912-2, time segment two 908-2; sub-channel two 912-2, time segment three908-3; etc. The 2D map is dynamically adjusted for each subscriberterminal 130 according to anticipated need by a scheduler in the SMTS.

Referring to FIG. 13, an embodiment of a channel diagram is shown. Onlythe channels for a single feeder spot beam 225 and a single service spotbeam 205 are shown, but embodiments include many of each spot beam 225,205 (e.g., various embodiments could have 60, 80, 100, 120, etc. of eachtype of spot beam 225, 205). The forward channel 800 includes n virtualchannels 808 traveling from the gateway antenna 110 to the service spotbeam 205. Each subscriber terminal 130 may be allocated one or more ofthe virtual channels 808. m MF-TDMA channels 912 make up the returnchannel 900 between the subscriber terminal (ST) antennas 125 and thefeeder spot beam 225.

Referring next to FIG. 3, an embodiment of a ground system 300 ofgateways 115 is shown in block diagram form. One embodiment could havefifteen active gateways 115 (and possibly spares) to generate sixtyservice spot beams, for example. The ground system 300 includes a numberof gateways 115 respectively coupled to antennas 110. All the gateways115 are coupled to a network 120 such as the Internet. The network isused to gather information for the subscriber terminals. Additionally,each SMTS communicates with other SMTS and the Internet using thenetwork 120 or other means not shown.

Each gateway 115 includes a transceiver 305, a SMTS 310 and a router325. The transceiver 305 includes both a transmitter and a receiver. Inthis embodiment, the transmitter takes a baseband signal and upconvertsand amplifies the baseband signal for transmission of the downstreamuplinks 135 with the antenna 110. The receiver downconverts and tunesthe upstream downlinks 140 along with other processing as explainedbelow. The SMTS 310 processes signals to allow the subscriber terminalsto request and receive information and schedules bandwidth for theforward and return channels 800, 900. Additionally, the SMTS 310provides configuration information and receives status from thesubscriber terminals 130. Any requested or returned information isforwarded via the router 325.

With reference to FIG. 11, an embodiment of gateway receiver 1100 isshown. This embodiment of the receiver 1100 processes four returnchannels 900 from four different service spot beams 205. The returnchannels 900 may be divided among four pathways using antennapolarization and/or filtering 1104. Each return channel is coupled to alow-noise amplifier (LNA) 1108. Down conversion 1112 mixes down thesignal into its intermediate frequency. Each of the upstreamsub-channels 912 is separated from the signal by a number of tuners1116. Further processing is performed in the SMTS 310.

Referring next to FIG. 10, an embodiment of a gateway transmitter 1000is shown. The downstream channels 800 are received at their intermediatefrequencies from the SMTS 310. With separate pathways, each downstreamchannel 800 is up-converted 1004 using two different carrierfrequencies. A power amplifier 1008 increases the amplitude of theforward channel 900 before coupling to the antenna 110. The antenna 110polarizes the separate signals to keep the four forward channels 800distinct as they are passed to the satellite 105.

With reference to FIG. 4, an embodiment of a SMTS 310 is shown in blockdiagram form. Baseband processing is done for the inbound and outboundlinks 135, 140 by a number of geographically separated gateways 115.Each SMTS 310 is generally divided into two sections, specifically, thedownstream portion 305 to send information to the satellite 105 and theupstream portion 315 to receive information from the satellite 105.

The downstream portion 305 takes information from the switching fabric416 through a number of downstream (DS) blades 412. The DS blades 412are divided among a number of downstream generators 408. This embodimentincludes four downstream generators 408, with one for each of thedownstream channels 800. For example, this embodiment uses four separate500 MHz spectrum ranges having different frequencies and/orpolarizations. A four-color modulator 436 has a modulator for eachrespective DS generator 408. The modulated signals are coupled to thetransmitter portion 1000 of the transceiver 305 at an intermediatefrequency. Each of the four downstream generators 408 in this embodimenthas J virtual DS blades 412.

The upstream portion 315 of the SMTS 310 receives and processesinformation from the satellite 105 in the baseband intermediatefrequency. After the receiver portion 1100 of the transceiver 305produces all the sub-channels 912 for the four separate basebandupstream signals, each sub-channel 912 is coupled to a differentdemodulator 428. Some embodiments could include a switch before thedemodulators 428 to allow any return link sub-channel 912 to go to anydemodulator 428 to allow dynamic reassignment between the four returnchannels 908. A number of demodulators are dedicated to an upstream (US)blade 424.

The US blades 424 serve to recover the information received from thesatellite 105 before providing it to the switching fabric 416. The USscheduler 430 on each US blade 424 serves to schedule use of the returnchannel 900 for each subscriber terminal 130. Future needs for thesubscriber terminals 130 of a particular return channel 900 can beassessed and bandwidth/latency adjusted accordingly in cooperation withthe Resource Manager and Load Balancer (RM/LB) block 420.

The RM/LB block 420 assigns traffic among the US and DS blades. Bycommunication with other RM/LB blocks 420 in other SMTSes 310, eachRM/LB block 420 can reassign subscriber terminals 130 and channels 800,900 to other gateways 115. This reassignment can take place for anynumber of reasons, for example, lack of resources and/or loadingconcerns. In this embodiment, the decisions are done in a distributedfashion among the RM/LB blocks 420, but other embodiments could havedecisions made by one master MR/LB block or at some other centraldecision-making authority. Reassignment of subscriber terminals 130could use overlapping service spot beams 205, for example.

Referring next to FIG. 5, an embodiment of a satellite 105 is shown inblock diagram form. The satellite 105 in this embodiment communicateswith fifteen gateways 115 and all STs 130 using sixty feeder and servicespot beams 225, 205. Other embodiments could use more or lessgateways/spot beams. Buss power 512 is supplied using a power sourcesuch as chemical fuel, nuclear fuel and/or solar energy. A satellitecontroller 516 is used to maintain attitude and otherwise control thesatellite 105. Software updates to the satellite 105 can be uploadedfrom the gateway 115 and performed by the satellite controller 516.

Information passes in two directions through the satellite 105. Adownstream translator 508 receives information from the fifteen gateways115 for relay to subscriber terminals 130 using sixty service spot beams205. An upstream translator 504 receives information from the subscriberterminals 130 occupying the sixty spot beam areas and relays thatinformation to the fifteen gateways 115. This embodiment of thesatellite can switch carrier frequencies in the downstream or upstreamprocessors 508, 504 in a “bent-pipe” configuration, but otherembodiments could do baseband switching between the various forward andreturn channels 800, 900. The frequencies and polarization for each spotbeam 225, 205 could be programmable or preconfigured.

With reference to FIG. 6A, an embodiment of an upstream translator 504is shown in block diagram form. A Receiver and Downconverter (Rx/DC)block 616 receives all the return link information for the area definedby a spot beam 205 as an analog signal before conversion to anintermediate frequency (IF). There is a Rx/DC block 616 for each servicespot beam area 205. An IF switch 612 routes a particular baseband signalfrom a Rx/DC block 616 to a particular upstream downlink channel. Theupstream downlink channel is filled using an Upconverter and TravelingWave Tube Amplifier (UC/TWTA) block 620. The frequency and/orpolarization can be changed through this process such that each upstreamchannel passes through the satellite 105 in a bent pipe fashion.

Each gateway 115 has four dedicated UC/TWTA blocks 620 in the upstreamtranslator 504. Two of the four dedicated UC/TWTA blocks 620 operate ata first frequency range and two operate at a second frequency range inthis embodiment. Additionally, two use right-hand polarization and twouse left-hand polarization. Between the two polarizations and twofrequencies, the satellite 105 can communicate with each gateway 115with four separate upstream downlink channels.

Referring next to FIG. 6B, an embodiment of a downstream translator 508is shown as a block diagram. Each gateway 115 has four downstream uplinkchannels to the satellite 105 by use of two frequency ranges and twopolarizations. A Rx/DC block 636 takes the analog signal and convertsthe signal to an intermediate frequency. There is a Rx/DC block 636 forall sixty downstream uplink channels from the fifteen gateways 115. TheIF switch 612 connects a particular channel 800 from a gateway 115 to aparticular service spot beam 205. Each IF signal from the switch 628 ismodulated and amplified with a UC/TWTA block 632. An antenna broadcaststhe signal using a spot beam to subscriber terminals 130 that occupy thearea of the spot beam. Just as with the upstream translator 504, thedownstream translator 508 can change carrier frequency and polarizationof a particular downstream channel in a bent-pipe fashion.

FIG. 7 comprises a block diagram illustrating a set of subscriberequipment 700 which may be located at a subscriber location for thereception and transmission of communication signals. Components of thisset of subscriber equipment 700 may, for example, comprise the antenna125, associated subscriber terminal 130 and any consumer premisesequipment (CPE) 160, which may be a computer, a network, etc.

An antenna 125 may receive signals from a satellite 105. The antenna 125may comprise a VSAT antenna, or any of a variety other antenna types(e.g., other parabolic antennas, microstrip antennas, or helicalantennas). In some embodiments, the antenna 125 may be configured todynamically modify its configuration to better receive signals atcertain frequency ranges or from certain locations. From the antenna125, the signals are forwarded (perhaps after some form of processing)to the subscriber terminal 130. The subscriber terminal 130 may includea radio frequency (RF) frontend 705, a controller 715, a virtual channelfilter 702, a modulator 725, a demodulator 710, a filter 706, adownstream protocol converter 718, an upstream protocol converter 722, areceive (Rx) buffer 712, and a transmit (Tx) buffer 716.

In this embodiment, the RF frontend 705 has both transmit and receivefunctions. The receive function includes amplification of the receivedsignals (e.g., with a low noise amplifier (LNA)). This amplified signalis then downconverted (e.g., using a mixer to combine it with a signalfrom a local oscillator (LO)). This downconverted signal may beamplified again with the RF frontend 705, before processing of thesuperframe 804 with the virtual channel filter 702. A subset of eachsuperframe 804 is culled from the downstream channel 800 by the virtualchannel filter 702, for example, one or more virtual channels 808 arefiltered off for further processing.

A variety of modulation and coding techniques may be used at thesubscriber terminal 130 for signals received from and transmitted to asatellite. In this embodiment, modulation techniques include BPSK, QPSK,8PSK, 16APSK, 32PSK. In other embodiments, additional modulationtechniques may include ASK, FSK, MFSK, and QAM, as well as a variety ofanalog techniques. The demodulator 710 may demodulate the down-convertedsignals, forwarding the demodulated virtual channel 808 to a filter 706to strip out the data intended for the particular subscriber terminal130 from other information in the virtual channel 808.

Once the information destined for the particular subscriber terminal 130is isolated, a downstream protocol converter 718 translates the protocolused for the satellite link into one that the DOCSIS MAC block 726 uses.Alternative embodiments could use a WiMAX MAC block or a combinationDOCSIS/WiMAX block. A Rx buffer 712 is used to convert the high-speedreceived burst into a lower-speed stream that the DOCSIS MAC block 726can process. The DOCSIS MAC block 726 is a circuit that receives aDOCSIS stream and manages it for the CPE 160. Tasks such asprovisioning, bandwidth management, access control, quality of service,etc. are managed by the DOCSIS MAC block 726. The CPE can ofteninterface with the DOCSIS MAC block 726 using Ethernet, WiFi, USB and/orother standard interfaces. In some embodiments, a WiMax block 726 couldbe used instead of a DOCSIS MAC block 726 to allow use of the WiMaxprotocol.

It is also worth noting that while a downstream protocol converter 718and upstream protocol converter 722 may be used to convert receivedpackets to DOCSIS or WiMax compatible frames for processing by a MACblock 726, these converters will not be necessary in many embodiments.For example, in embodiments where DOCSIS or WiMax based components arenot used, the protocol used for the satellite link may also becompatible with the MAC block 726 without such conversions, and theconverters 718, 722 may therefore be excluded.

Various functions of the subscriber terminal 130 are managed by thecontroller 715. The controller 715 may oversee a variety of decoding,interleaving, decryption, and unscrambling techniques, as known in theart. The controller may also manage the functions applicable to thesignals and exchange of processed data with one or more CPEs 160. TheCPE 160 may comprise one or more user terminals, such as personalcomputers, laptops, or any other computing devices as known in the art.

The controller 715, along with the other components of the subscriberterminal 130, may be implemented in one or more Application SpecificIntegrated Circuits (ASICs), or a general purpose processor adapted toperform the applicable functions. Alternatively, the functions of thesubscriber terminal 130 may be performed by one or more other processingunits (or cores), on one or more integrated circuits. In otherembodiments, other types of integrated circuits may be used (e.g.,Structured/Platform ASICs, Field Programmable Gate Arrays (FPGAs) andother Semi-Custom ICs), which may be programmed in any manner known inthe art. The controller may be programmed to access memory unit (notshown). It may fetch instructions and other data from the memory unit,or write data to the memory-unit.

As noted above, data may also be transmitted from the CPE 160 throughthe subscriber terminal 130 and up to a satellite 105 in variouscommunication signals. The CPE 160, therefore, may transmit data toDOCSIS MAC block 726 for conversion to the DOCSIS protocol before thatprotocol is translated with an upstream protocol converter 722. Theslow-rate data waits in the Tx buffer 716 until it is burst over thesatellite link.

The processed data is then transmitted from the Tx buffer 716 to themodulator 725, where it is modulated using one of the techniquesdescribed above. In some embodiments, adaptive or variable coding andmodulation techniques may be used in these transmissions. Specifically,different modulation and coding combinations, or “modcodes,” may be usedfor different packets, depending on the signal quality metrics from theantenna 125 to the satellite 105. Other factors, such as network andsatellite congestion issues, may be factored into the determination, aswell. Signal quality information may be received from the satellite orother sources, and various decisions regarding modcode applicability maybe made locally at the controller, or remotely. The RF frontend 705 maythen amplify and upconvert the modulated signals for transmissionthrough the antenna 125 to the satellite.

Satellite Architecture

According to an embodiment of the invention, a novel architecture ispresented for establishing a multi-beam satellite communication systemhaving both forward links and return links connecting gateways andsubscriber terminals. Such a multi-beam satellite communication systemis illustrated in the figures. For example, referring to FIGS. 1A and1B, a gateway 115 sends a forward link signal to one or more subscriberterminals 130-a through 130-n via satellite 105. Here, a forward linkrefers to signals sent from a gateway to one or more subscriberterminals. Such gateway-to-subscriber signals are also sometimesreferred to as downstream signals. In the reverse direction, the one ormore subscriber terminals 130-a through 130-n send one or more returnlink signals to gateway 115. Such subscriber-to-gateway signals are alsosometimes referred to as upstream signals.

One of the many uses of the systems such as that shown in FIGS. 1A and1B may be to provide network access (e.g., Internet access) to thesubscriber terminals. For example, a subscriber terminal 130-a mayrequest a web page on the Internet by sending a network request using areturn link (upstream) signal (145-a, 140) to gateway 115 via satellite105. Gateway 115 responds by retrieving the requested web page fromnetwork 120, which may directly or indirectly connected to the Internet.Gateway 115 then sends the requested web page using a forward link(downstream) signal (135, 150) to subscriber terminal 130-a viasatellite 105, thus completing the web page request and response.Different layers of networking protocol operations may be implemented inthe process, as is known to one of ordinary skill in the art.

According to the present embodiment of the invention, satellite 105comprises a bent pipe repeater that is capable of receiving one or moresignals from Earth and transmitting the signals back toward Earth,possibly after frequency translation and polarization modification. Forexample, each signal received at satellite 105 at a particular frequencyand polarization may be transmitted out of satellite 105 at a differentfrequency and/or polarization. The bent pipe repeater may also provideswitching operations, such that different “feeder signals” (i.e.,signals sent to and from gateways) may be switched to be connected todifferent “service signals” (i.e., signals sent to and from subscriberterminals). The bent pipe repeater does not demodulate signals receivedat the satellite into data such as bits and re-modulate the data fortransmission. This is in contrast to processing repeaters, which arecapable of performing such demodulation and re-modulation to achievegains in error correction performance. Even though processing repeatersare commercially available, a bent pipe repeater is adopted to achieveoptimal efficiency in forward link and return link communications inaccordance with the present embodiment of the invention.

Referring to FIG. 6B, satellite components for handling forward links inthe downstream direction from gateways to subscriber terminals may beimplemented as shown in accordance with one embodiment of the invention.Here, 15 gateways together send 60 forward link signals to thesatellite. Specifically, each gateway sends an uplink feeder beamcomprising 4 different forward link signals utilizing an antenna. Eachof the 4 forward link signals is transmitted using a differentcombination of frequency band and polarization. Each unique combinationis referred to as a specific “color,” as discussed previously. Eachforward link signal is received at the satellite at a particularreceiver module 636. Each receiver module 636 may include a receiversuch as a low noise amplifier (LNA) followed by a downconverter (DC)that converts the forward link signal to a convenient frequency, such asan intermediate frequency (IF).

According to an embodiment of the invention, each forward link signal isa broadband signal. Here, the term “broadband” is used in the context ofsatellite communications and specifically refers to a signal having abandwidth of at least 250 MHz. For example, in the present embodiment,each forward link signal is a broadband signal and has a bandwidth of500 MHz.

Each forward link signal is then connected through a switch 628 to anappropriate transmit module 632. Transmit module may include anupconverter (UC) that up-converts the IF forward link signal to afrequency suitable for transmission, followed by a satellite-basedtransmission amplifier. According to an embodiment of the invention, thesatellite-based transmission amplifier may be a traveling wave tubeamplifier (TWTA), which efficiently amplifies the signal as asingle-carrier signal. Here, each satellite-based transmission amplifieris employed to amplify only one single-carrier signal, which allows theamplifier to be operated more efficiently. This design allows highlyefficient use of the satellite-based transmission amplifiers.

Thus, each satellite-based transmission amplifier produces an amplifiedsingle-carrier signal that may then be transmitted out using an antennato form a spot beam that reaches Earth. The spot beam thus has an earthsurface coverage area. Subscriber terminals that are within thisparticular earth surface coverage area would be able to receive theforward link signal. Here, each spot beam is formed by the output of asingle satellite-based transmission amplifier. In other words, there isno need to combined the outputs of multiple transmission amplifiers toform each spot beam. This precludes power losses and allows thesatellite-based transmission amplifiers to be operated even moreefficiently.

The novel use of a single carrier signal per satellite-basedtransmission amplifier and a single satellite-based transmissionamplifier per spot beam aboard a bent pipe repeater optimizes the ratioof data capacity to power consumption at the satellite, to obtainsignificant improvements in performance from satellite equipment.

Frequency Re-Use for Service and Gateway Beams

According to an embodiment of the invention, a satellite system ispresented that adopts multiple levels of frequency re-use to maximizeusage of available frequency bandwidth. In addition to employingfrequency re-use amongst multiple service beams such that differentservice beams may occupy a common frequency channel, the system furtheremploys frequency re-use between service beams and feeder beams bylocating gateways in regions separated from coverage areas of servicebeams. In addition, frequency re-use may also be employed amongstmultiple feeder beams to allow further gains in spectral efficiency.Such multiple levels of frequency re-use is explained in more detail inan illustrative system as discussed below.

Referring to the example systems depicted in FIGS. 6A and 6B, a starnetwork includes 15 independent feeder beams to support 60 servicebeams. Thus, each feeder beam corresponds to four service beams. Here,this ratio is maintained in both the uplink and downlink direction. Inthe forward direction, every uplink feeder beam is relayed by thesatellite to generate four downlink service beams. In the returndirection, every four uplink service beams are relayed by the satelliteto generate one downlink feeder beam. Thus, the star network can beviewed as having 15 groups of signals, each group containing one uplinkfeeder beam, one downlink feeder beam, four uplink service beams, andfour downlink service beams.

Next, four uplink service beams 4006 are shown as being sent fromsubscriber terminals to the satellite. Here, the same 4 colors used totransmit uplink feeder beam 4002 may be re-used to transmit the fouruplink service beams 4008. Specifically, these 4 colors are formed usingtwo different 500 MHz uplink frequency channels, 27.5 GHz-28 GHz and29.5 GHz-30 GHz, along with two different polarizations, RHCP and LHCP.This is possible because the gateway sending uplink feeder beam 4002 ispositioned at a different location on Earth than the subscriberterminals sending uplink service beams 4006. Directional antennas on thesatellite are therefore able to separately receive uplink feeder beam4002 and uplink service beams 4006, even though they may be transmittedusing the same uplink frequencies and polarizations. In addition,because the four uplink service beams possess spatial diversity amongstthemselves, which facilitates frequency re-use, different options existfor how these 4 colors may be used to transmit uplink service beams4006. For example, all 4 colors may be used, or just 2 colors may beused, or some variation may be adopted. The situation is similar to thatdiscussed above with respect to the four downlink service beams 4004.

First, an uplink feeder beam 4002 comprising 4 carriers is shown asbeing sent from a gateway terminal to the satellite, by utilizing 4different combinations of frequency and polarization (4 “colors”) asdescribed previously. Here, these 4 colors are formed using twodifferent 500 MHz uplink frequency channels, 27.5 GHz-28 GHz and 29.5GHz-30 GHz, along with two different polarizations, right hand circularpolarization (RHCP) and left hand circular polarization (LHCP).

Next, four downlink service beams 4004 are shown as being sent from thesatellite to subscriber terminals. There are 4 colors shown, formedusing two different 500 MHz downlink frequency channels, 17.7 GHz-18.2GHz and 19.7 GHz-20.2 GHz, along with two different polarizations RHCPand LHCP. Here, because the four downlink service beams possess spatialdiversity amongst themselves, which facilitates frequency re-use,different options exist for how the 4 colors may be used. In oneimplementation, all four colors are used, each for a different downlinkservice beam. In another implementation, only two of the colors are usedfor the four downlink service beams. For example, the two colorsrepresenting (1) 17.7 GHz-18.2 GHz with LHCP and (2) 17.7 GHz-18.2 GHzwith RHCP may be used to transmit all four downlink service beams. Thus,the downlink service beams may be transmitted using the same 500 MHzbandwidth, but with alternating polarizations (LHCP and RHCP) assignedto physically adjacent downlink service beams, to allow closely spacedbeams to be distinguished from one another. Other variations arepossible and are within the scope of the present invention.

Next, four uplink service beams 4006 are shown as being sent fromsubscriber terminals to the satellite. Here, the same 4 colors used totransmit uplink feeder beam 4002 may be re-used to transmit the fouruplink service beams 4008. Specifically, these 4 colors are formed usingtwo different 500 MHz uplink frequency channels, 27.5 GHz-28 GHz and29.5 GHz-30 GHz, along with two different polarizations, RHCP and LHCP.This is possible because the gateway sending uplink feeder beam 4002 ispositioned at a different location on Earth than the subscriberterminals sending uplink service beams 4006. Directional antennas on thesatellite are therefore able to separately receive uplink feeder beam4002 and uplink service beams 4006, even though they may be transmittedusing the same uplink frequencies and polarizations. In addition,because the four uplink service beams possess spatial diversity amongstthemselves, which facilitates frequency re-use, different options existfor how these 4 colors may be used to transmit uplink service beams4006. For example, all 4 colors may be used, or just 2 colors may beused, or some variation may be adopted. The situation is similar to thatdiscussed above with respect to the four downlink service beams 4004.

Finally, a downlink feeder beam 4008 comprising 4 carriers is shown asbeing sent from the satellite to the gateway terminal. Here, the same 4colors used to transmit downlink service beams 4004 may be re-used totransmit the downlink feeder beam 4008. Specifically, these 4 colors areformed using two different 500 MHz downlink frequency channels, 17.7GHz-18.2 GHz and 19.7 GHz-20.2 GHz, along with two differentpolarizations RHCP and LHCP. This is possible because the gatewayreceiving downlink feeder beam 4008 is positioned at a differentlocation on Earth than the subscriber terminals receiving downlinkservice beams 4004. That is, the gateway is located in the feeder beamcoverage area where downlink feeder beam 4008 can be received.Separately, the subscriber terminals are located the service beamcoverage areas where downlink service beams 4004 can be received. Assuch, downlink feeder beam 4008 and downlink service beams 4004 canre-use the same downlink frequencies and polarizations, yet still beseparately received by the intended recipients.

As mentioned previously, the same frequency re-use plan 400 may beapplied to each of the 15 groups of signals. That is, the entire systemcomprising 15 uplink feeder beams, 60 downlink service beams, 60 uplinkservice beams, and 15 downlink feeder beams may simultaneously adopt thesame frequency re-use plan 400. This is achieved by capitalizing onspatial diversity that may exist amongst the 60 service beam coverageareas, positioning the 15 feeder beam coverage areas sufficiently faraway from the 60 service beam coverage areas, and positioning the 15feeder beam coverage areas sufficiently far apart from one another.Accordingly, three different levels of frequency re-use are realized.First, frequency re-use is achieved amongst service beams. Second,frequency re-use is achieved between service beams and feeder beams.Third, frequency re-use is achieved amongst feeder beams.

Placement of Gateways Away from Service Beams

According to an embodiment of the invention, a satellite system ispresented having efficient placement of gateway terminals. As discussedpreviously, spatial diversity between gateways and subscriber terminalsfacilitates frequency re-use of between service beams and feeder beams.Also, spatial diversity amongst gateways facilitates frequency re-useamongst feeder beams. Placement of the gateways may take into accountthese and other considerations.

In one embodiment, the plurality of different service beam coverageareas (e.g., 60 service beam coverage areas) may be designed to onlyprovide strategically chosen partial coverage over a coverage region.Generally speaking, typical satellite systems that providecommunications over a geographic region attempt to achieve full coveragesuch that service is available over the entire region. However, inaccordance with the present embodiment of the invention, a satellitesystem may be designed to only provide strategically chosen partialcoverage over a particular region. For example, the coverage region maycomprise a region including the western, eastern, and southern portionsof the United States. The specific coverage areas supported by theservice beams may be chosen in different ways. For example, the coverageareas may correspond to “underserved” locations, where there may existsignificant populations but where high bandwidth network access is notyet readily available.

According to an embodiment of the present invention, the one or moregateways are placed away from the coverage areas of the service beams,to facilitate frequency re-use between service beams and feeder beams.In the example system discussed earlier, suppose the 60 uplink anddownlink service beams have coverage areas in a region that spans thewestern, eastern, and southern portions of the United States. Then the15 gateways may be located in a region, such as the middle portion ofthe United States, away from the coverage region of the service beams.

In addition, a plurality of gateways (e.g., 15 gateways) may need to belocated sufficiently far apart from each other such that frequencyre-use may be further adopted amongst different feeder beams. Forinstance, each gateway may need to be placed such that has a minimumdistance of 400 kilometers from any neighboring gateway. Thus,neighboring gateways may use the same frequency channels withoutinterfering with one another.

A further possible constraint on the placement of the gateways relatesto physical proximity to higher bandwidth network access. For example,gateways may be located near optical fiber network connections. Thisallows the gateways to have fast and robust network access such thatdata communications requiring access to networks is not hindered.According to one embodiment of the invention, in addition to otherrequirements, each gateway is placed within a distance of 50 kilometersfrom an optical fiber network connection.

Yet another possible constraint on the placement of the gateways relatesto area weather patterns. Gateways may need to be located in areas thatexperience minimal rain fade. Just as an example, each gateway may berequired to be placed at a location where overall rain fade at theuplink frequency is less 10 dB of fading for 99.99% of the time. Thisfurther constrains the selection of possible locations for gatewayterminals.

Thus, in accordance with an embodiment of the present invention, theplacement of the gateways may take into account multiple factors such asthose described above. While meeting such multiple constraints can makethe placement of gateways significantly more challenging, a system thatadopts these constraints is likely to achieve superior overallperformance.

Piggy-Back Satellite Payload

According to one embodiment, a portion of the total bus power aboard acommunications satellite is used to support a version of the satellitecommunication system of the present invention. Referred to as a “piggyback” mode, this technique allows either an entire satellitecommunication system as described above, or a portion thereof, to besupported by a satellite that also carries other communications payload.For example, if a particular satellite has an available total bus powerof 15 kilowatts (KW), and the satellite already has an existing payloadthat consumes 13 KW of bus power, there may remain 2 KW of excess buspower aboard the satellite. According to one embodiment of theinvention, a satellite system as describe above, or a portion thereof,may be implemented by using the remaining 2 KW of bus power. Thus, anexample system of 8 service beams and 2 corresponding feeder beams inthe forward and return link directions may be deployed using the excess2 KW of bus power aboard the communication satellite described above.

The added payload may constitute an independent satellite communicationsystem. Alternatively, the added payload may constitute a fraction of asatellite system. For example, a full satellite system may employ 60service beams and 15 corresponding feeder beams in the forward link andthe return link direction, as discussed previously. A fraction of such asystem may correspond to the 8 service beams and 2 corresponding feederbeams in the forward and return link directions discussed above. Thefeatures of the full satellite system may be substantially representedin the fractional system.

The added payload may adopt a structure similar to that of anindependent satellite architecture as described in embodiments discussedpreviously. For example, in the forward link direction, each feeder beamsent from a gateway to the satellite may comprise 4 signals (representedby four “colors,” for instance) that produce 4 separate single-carriersignals sent from the satellite as separate service spot beams to reachsubscriber terminals. Other satellite architecture features maysimilarly be adopted for use in a system implemented as an addedpayload.

Different implementations are possible. One implementation is brieflydescribed below for illustrative purposes. Here, the added payloadcomprises a Ka package that can be added to an existing satelliteprocurement. Such a system may at a very high level enable trade-offs indesign that minimize the impact of the package on the physical designand layout, weight, and power on the overall satellite design. Anexample market for this added payload may be the consumer broadbandmarket. The package may be capable of 10 spot beams each of which isapproximately 0.35 degrees Half Power Beam Width (HPBW) on transmit andreceive. TWTA redundancy should be consistent with orbital life. Thesystem may have four color re-use with 2 of the 10 spot beams for feederlinks. The Effective Isotropic Radiated Power (EIRP) of the package maybe 70 dBW per spot beam and the G/T may be 27 dB/° K per spot beam. Theindividual transponders may be wide band on the order of 500 MHz.Polarization may be circular and alternate spots may use alternatelyLeft and Right Hand polarization. The input SFD may be settable from−105 to −85 dB in one dB steps.

According to the invention, differently sized payloads may be thus addedthrough use of “piggy back” mode to allow efficient use of excess buspower aboard satellites. Specific parameters such as the number of spotbeams implemented may be varied according to the needs of the system.

Adaptive Use of Satellite Uplink Bands

According to an embodiment of the invention, adaptive use of satelliteuplink bands is employed. One example implementation of such a techniqueallows flexible use of frequency channels by a subscriber terminal thatis a secondary spectrum license holder. The right of a secondaryspectrum license holder to transmit on a specified frequency band issecondary to that of a primary spectrum license holder. That is, theprimary spectrum license holder may be able to transmit signals on thefrequency band whenever it chooses, without regard for other users. Bycontrast, a secondary spectrum license holder may only be allowed totransmit on the specified frequency band if the primary spectrum licensehold is not transmitting on the specified band. Adaptive use ofsatellite uplink bands as described in various embodiments of thepresent invention may be utilized by a subscriber terminal which is asecondary spectrum holder, to ensure that when another signal, e.g., theprimary license holder's signal, is detected, re-assignment of thetransmit frequency channel can be performed to move satellite uplinktransmission to a different frequency as to not interfere with theprimary spectrum license holder.

FIG. 15 presents an illustrative system employing adaptive use ofsatellite uplink bands in accordance with one embodiment of theinvention. Here, a central unit 121 controls the assignment of transmitfrequency channels and receive frequency channels used by subscriberterminals such as 130-a-1 and 130-a-2. Central unit 121 may be coupledto a gateway 115 through network 120. Central unit 121 may thus beconnected to other gateways as well, in order to control a largersatellite system. In an alternative embodiment, central unit 121 may becontained in a gateway such as gateway 115.

Central unit 121 assigns to subscriber terminal 130-a-1 a transmitfrequency channel in which to transmit satellite uplink signals 145-a-1,as well a receive frequency channel in which to receive satellitedownlink signals 150. Similarly, central unit 121 assigns to subscriberterminal 130-a-2 a transmit frequency channel in which to transmitsatellite uplink signals 145-a-2, as well as a receive frequency channelin which to receive satellite downlink signals 150. According to anembodiment of the invention, central unit 121 may employ an adoptivescheme to assign transmit frequency channels to one or more subscriberterminals, based on local observations of the transmit frequencyspectrum made by the subscriber terminals and reported back to thecentral unit 121, as discussed below.

Subscriber terminal 130-a-1's transmission of satellite uplink signals145-a-1 in the assigned transmit frequency channel may be intermittentin nature. For example, the uplink signals may carry web page requeststhat only require short bursts of data. Thus, the satellite uplinksignals may be sent during time-separated periods of transmission. Thatis, each period of transmission may be limited in duration. The periodsof transmission may be separated by time in which no transmission issent from subscriber terminal 130-a-1.

Subscriber terminal 130-a-1 may monitor the assigned transmit frequencychannel between these time-separated periods of transmission ofsatellite uplink signals. That is, when subscriber terminal 130-a-1 isnot transmitting, it can monitor the assigned transmit frequency channelfor possible presence of other signals from outside sources. There maybe different types of such outside sources, such as a Land Mobile DataServices (LMDS) user 127. One context in which such a scenario couldarise is when central unit 121 assigns a transmit frequency channel thatutilizes bandwidth in which the LMDS user 127 is the primary spectrumlicense holder, and subscriber terminal 130-a-1 is a secondary spectrumlicense holder. As such, subscriber terminal 130-a-1 may not use theassigned transmit frequency channel if the LMDS user 127 is using thechannel.

In addition to monitoring the assigned transmit frequency channel,subscriber terminal 130-a-1 may also monitor at least one out-of-bandfrequency channel different from the assigned transmit frequencychannel. For example, subscriber terminal 130-a-1 may also monitor oneor more neighboring frequency channels. The neighboring frequencychannels may include a number of channels in the vicinity of theassigned transmit frequency channel. These may include channels that areimmediately adjacent to the currently assigned transmit frequencychannel, as well as other channels. Monitoring of out-of-band frequencychannels facilitates detection of other signals, such as signal 128,over a wider range of frequencies. This information allows a morecomplete picture to be formed regarding the spectrum that canpotentially be used by subscriber terminal 130-a-1 for signaltransmission.

In one embodiment, subscriber terminal 130-a-1 transmits and receivessatellite signals using a first antenna 125-a-1, and performs monitoringof frequency channels using a second antenna 126-a-1. Here, this dualantenna arrangement allows for easier implementation. The first antenna125-a-1 may be a parabolic reflective antenna pointed toward satellite150. Thus, the first antenna is suited for transmitting and receivingsatellite signals. The second antenna 126-a-2 may be a dipole antennadesigned for terrestrial signals. The second antenna may be well suitedfor detecting terrestrial signals that travel in the direction along thehorizon, such as a signal 128 sent from LMDS user 127. This is merelyone example arrangement. Variations may be implemented within the scopeof the invention.

When a signal such as signal 128 from the LMDS user 127 is detected,subscriber terminal 130-a-1 notifies central unit 121. This may be doneusing an observation result reported back to central unit 121. Theobservation result may be generated in different ways. As one example,subscriber terminal 130-a-1 may generate observation resultautomatically on a periodic basis. As another example, central unit 121may request observation results from subscriber terminal 130-a-1 atappropriate times. Also, an observation result may be reported indifferent formats, depending on implementation. The format may a Booleanvalue, a numeric value, etc. In one implementation, an observationresult is sent regardless of whether presence of another signal isdetected. In an alternative implementation, an observation result isonly sent if presence of another signal is detected.

In response, central unit 121 may re-assign subscriber terminal 130-a-1to a different transmit frequency channel, in order to avoid interferingwith the source of the detected signal. In this case, the frequencyre-assignment serves to prevent interference with signal 128 sent byLMDS user 127, which may be the primary spectrum license holder. Centralunit 121 may determine the new transmit frequency channel for subscriberterminal 130-a-1 in different ways. In certain embodiments, thedetermination is a simple one that does not take into considerationmonitoring performed at other subscriber terminals. For example, theremay be a default frequency channel that is assigned.

In other embodiments, the determination does take into accountmonitoring performed at other subscriber terminals. Some or all of thesubscriber terminals may perform frequency channel monitoring and reportobservation results back to central unit 121. Central unit 121 may thendecide on an overall frequency assignment that considers the needs of aplurality of subscriber terminals. Thus, the determination of a newlyassigned transmit frequency channel for each subscriber terminal may bemade as part of the overall frequency assignment. A simple example isdescribed below for illustrative purposes.

Suppose subscriber terminal 130-a-1 is currently assigned to transmitsatellite uplink signals on frequency channel X and reports that itobserves that frequency channel X and most other frequency channels arebeing used by other signals (such as signal 128 from an LMDS user), andthat only one particular frequency channel Y appears to be unused byother signals. Further suppose that subscriber terminal 130-a-2 iscurrently assigned to transmit satellite uplink signals on frequencychannel Y and reports that it observes that frequency channel Y and mostother frequency channels are not being used by other signals. Inresponse, central unit 121 may determine that the best overall frequencyassignment would involve re-assigning subscriber terminal 130-a-2 to atransmit frequency channel other than Y, so that channel Y can beassigned to subscriber terminals 130-a-1. For instance, subscriberterminal 130-a-2 may be re-assigned to frequency channel X, andsubscriber terminal 130-a-1 may be re-assigned to frequency channel Y.This allows both subscriber terminals to operate without interferingwith other signals that may represent primary spectrum license holders,by taking into account the observations made at both subscriberterminals to arrive at a joint frequency plan for the subscriberterminals. Of course, this is only a simple example involving twosubscriber terminals. Frequency assignments involving more subscriberterminals are within the scope of the present invention.

It should be noted that the systems, methods, and software discussedabove are intended merely to be exemplary in nature. It must be stressedthat various embodiments may omit, substitute, or add various proceduresor components as appropriate. For instance, it should be appreciatedthat in alternative embodiments, the methods may be performed in anorder different than that described, and that various steps may beadded, omitted or combined. Also, features described with respect tocertain embodiments may be combined in various other embodiments.Different aspects and elements of the embodiments may be combined in asimilar manner. Also, it should be emphasized that technology evolvesand, thus, many of the elements are exemplary in nature and should notbe interpreted to limit the scope of the invention.

Specific details are given in the description to provide a thoroughunderstanding of the embodiments. However, it will be understood by oneof ordinary skill in the art that the embodiments may be practicedwithout these specific details. For example, well-known circuits,processes, algorithms, structures, and techniques have been shownwithout unnecessary detail in order to avoid obscuring the embodiments.

Also, it is noted that the embodiments may be described as a processwhich is depicted as a flow chart, a structure diagram, or a blockdiagram. Although they may describe the operations as a sequentialprocess, many of the operations can be performed in parallel orconcurrently. In addition, the order of the operations may bere-arranged. A process is terminated when its operations are completed,but could have additional steps not included in the figure.

Moreover, as disclosed herein, the terms “storage medium” or “storagedevice” may represent one or more devices for storing data, includingread only memory (ROM), random access memory (RAM), magnetic RAM, corememory, magnetic disk storage mediums, optical storage mediums, flashmemory devices or other computer readable mediums for storinginformation. The term “computer-readable medium” includes, but is notlimited to, portable or fixed storage devices, optical storage devices,wireless channels, a sim card, other smart cards, and various othermediums capable of storing, containing or carrying instructions or data.

Furthermore, embodiments may be implemented by hardware, software,firmware, middleware, microcode, hardware description languages, or anycombination thereof. When implemented in software, firmware, middlewareor microcode, the program code or code segments to perform the necessarytasks may be stored in a machine readable medium such as a storagemedium. Processors may perform the necessary tasks.

Having described several embodiments, it will be recognized by those ofskill in the art that various modifications, alternative constructions,and equivalents may be used without departing from the spirit of theinvention. For example, the above elements may merely be a component ofa larger system, wherein other rules may take precedence over orotherwise modify the application of the invention. Also, a number ofsteps may be required before the above elements are considered.Accordingly, the above description should not be taken as limiting thescope of the invention, which is defined in the following claims.

What is claimed is:
 1. A method for communicating data in ageosynchronous satellite system, the method comprising: receiving at ageosynchronous satellite a plurality of uplink service beams, each ofthe plurality of uplink service beams being associated with a differentservice beam coverage area which together form a combined service beamcoverage area; transmitting, by the geosynchronous satellite, aplurality of downlink service beams to a plurality of user terminals, atleast one of the plurality of downlink service beams being transmittedusing a common downlink frequency and a common downlink polarization;receiving, at the geosynchronous satellite, an uplink feeder beam from agateway located within a feeder beam coverage area at least partiallynot overlapping the combined service beam coverage area and, in responseto receiving the uplink feeder beam, forming the plurality of downlinkservice beams; and forming a downlink feeder beam responsive to theplurality of uplink service beams and transmitting, by thegeosynchronous satellite, the downlink feeder beam using the commondownlink frequency and the common downlink polarization.
 2. The methodof claim 1 further comprising transmitting, by the geosynchronoussatellite, an additional downlink feeder beam using the common downlinkfrequency and the common downlink polarization.
 3. The method of claim 2wherein the downlink feeder beam and the additional downlink feeder beamare transmitted by the geosynchronous satellite to two gateways that areseparated from each other by a minimum distance of 400 kilometers. 4.The method of claim 1 wherein the downlink feeder beam comprises twofrequency channels, each of the two frequency channels separated byright hand circular polarization (RHCP) and left hand circularpolarization (LHCP), to form four unique combinations of frequency andpolarization, and wherein one of the four unique combinations uses thecommon downlink frequency and the common downlink polarization.
 5. Themethod of claim 4 wherein at least one of the two frequency channelsincludes a 500 MHz frequency channel.
 6. The method of claim 1 whereinthe plurality of downlink service beams are transmitted using downlinkfrequency channels comprising two frequency channels, each of the twofrequency channels separated by right hand circular polarization (RHCP)and left hand circular polarization (LHCP), to form four uniquecombinations of frequency and polarization, wherein each downlinkservice beam is transmitted using one of the four unique combinations offrequency and polarization, and wherein at least one of the downlinkservice beams is transmitted using the common downlink frequency and thecommon downlink polarization.
 7. A geosynchronous satellite forcommunicating data, the geosynchronous satellite comprising: a firstreceiver for receiving a plurality of uplink service beams, each of theplurality of uplink service beams being associated with a differentservice beam coverage area which together form a combined service beamcoverage area; a first transmitter for transmitting a plurality ofdownlink service beams to a plurality of user terminals, the firsttransmitter for transmitting at least one of the plurality of downlinkservice beams using a common downlink frequency and a common downlinkpolarization; a second receiver for receiving an uplink feeder beam froma gateway located within a feeder beam coverage area at least partiallynot overlapping the combined service beam coverage area; a processorcoupled to the first and second receivers and the first transmitter andfor forming the plurality of downlink service beams responsive toreceiving the uplink feeder beam and for forming a downlink feeder beamresponsive to receiving the plurality of uplink service beams; and asecond transmitter coupled to the processor and for transmitting thedownlink feeder beam using the common downlink frequency and the commondownlink polarization.
 8. The geosynchronous satellite of claim 7wherein the second transmitter is for further transmitting an additionaldownlink feeder beam using the common downlink frequency and the commondownlink polarization.
 9. The geosynchronous satellite of claim 8wherein the downlink feeder beam and the additional downlink feeder beamare transmitted by the geosynchronous satellite to two gateways that areseparated from each other by a minimum distance of 400 kilometers. 10.The geosynchronous satellite of claim 7 wherein the downlink feeder beamcomprises two frequency channels, each of the two frequency channelsseparated by right hand circular polarization (RHCP) and left handcircular polarization (LHCP), to form four unique combinations offrequency and polarization, and wherein one of the four uniquecombinations uses the common downlink frequency and the common downlinkpolarization.
 11. The geosynchronous satellite of claim 10 wherein atleast one of the two frequency channels includes a 500 MHz frequencychannel.
 12. The geosynchronous satellite of claim 8 wherein theplurality of downlink service beams are transmitted using downlinkfrequency channels comprising two frequency channels, each of the twofrequency channels separated by right hand circular polarization (RHCP)and left hand circular polarization (LHCP), to form four uniquecombinations of frequency and polarization, wherein each downlinkservice beam is transmitted using one of the four unique combinations offrequency and polarization, and wherein at least one of the downlinkservice beams is transmitted using the common downlink frequency and thecommon downlink polarization.
 13. A system for communicating data in amultibeam satellite system utilizing frequency re-use comprising: meansfor establishing service beams including uplink service beams anddownlink service beams between a satellite and a plurality of subscriberterminals, each downlink service beam being associated with a differentservice beam coverage area which together form a combined service beamcoverage area; wherein a plurality of the uplink service beams aretransmitted to the satellite, and a plurality of the downlink servicebeams are transmitted from the satellite, at least two of the pluralityof the downlink service beams being transmitted using a common downlinkfrequency and a common downlink polarization; means for establishing atleast one uplink feeder beam and at least one downlink feeder beambetween the satellite and a gateway terminal, the at least one downlinkfeeder beam being associated with a feeder beam coverage area at leastpartially not overlapping the combined service beam coverage area, theat least one uplink feeder beam being received at the satellite to forma plurality of the downlink service beams, a plurality of the uplinkservice beams being received at the satellite to form the at least onedownlink feeder beam; and wherein the at least one uplink feeder beam istransmitted to the satellite, and the at least one downlink feeder beamis transmitted from the satellite by re-using the common downlinkfrequency and the common downlink polarization.
 14. A geosynchronoussatellite for communicating data, the geosynchronous satellitecomprising: first receiving means for receiving a plurality of uplinkservice beams, each of the plurality of uplink service beams beingassociated with a different service beam coverage area which togetherform a combined service beam coverage area; first transmitting means fortransmitting a plurality of downlink service beams to a plurality ofuser terminals, the first transmitting means for transmitting at leastone of the plurality of downlink service beams using a common downlinkfrequency and a common downlink polarization; second receiving means,coupled to the first transmitting means, for receiving an uplink feederbeam from a gateway located within a feeder beam coverage area at leastpartially not overlapping the combined service beam coverage area and,in response to receiving the uplink feeder beam, forming the pluralityof downlink service beams; and second transmitting means, coupled to thefirst receiving means, for forming a downlink feeder beam responsive tothe plurality of uplink service beams and transmitting the downlinkfeeder beam using the common downlink frequency and the common downlinkpolarization.
 15. A geosynchronous satellite system comprising: aplurality of user terminals for establishing composite service beamsincluding uplink service beams and downlink service beams between theuser terminals and a geosynchronous satellite, each downlink servicebeam being associated with a different service beam coverage area whichtogether form a combined service beam coverage area, at least one of theplurality of user terminals for establishing a composite service beamincluding a downlink service beam using a common downlink frequency anda common downlink polarization; and a gateway for establishing an uplinkfeeder beam corresponding to the downlink service beams, and forestablishing a downlink feeder beam associated with the uplink servicebeams using the common downlink frequency and the common downlinkpolarization, between the gateway and the geosynchronous satellite, thedownlink feeder beam being associated with a feeder beam coverage areaat least partially not overlapping the combined service beam coveragearea.
 16. A geosynchronous satellite comprising: a downstream translatorfor: receiving an uplink feeder beam, forming a plurality of downlinkservice beams between the geosynchronous satellite and a plurality ofuser terminals, the plurality of downlink service beams formed from theuplink feeder beam, each downlink service beam being associated with adifferent service beam coverage area which together form a combinedservice beam coverage area, and transmitting the downlink service beamsfrom the geosynchronous satellite, at least one of the downlink servicebeams transmitted using a common downlink frequency and a commondownlink polarization; and an upstream translator for: receiving aplurality of uplink service beams, forming a downlink feeder beambetween the geosynchronous satellite and a gateway, the downlink feederbeam formed from the plurality of uplink service beams, the downlinkfeeder beam being associated with a feeder beam coverage area at leastpartially not overlapping the combined service beam coverage area, andtransmitting the downlink feeder beam from the geosynchronous satelliteusing the common downlink frequency and the common downlinkpolarization.
 17. A geosynchronous satellite comprising: means forestablishing a plurality of composite service beams between thegeosynchronous satellite and a plurality of user terminals, eachcomposite service beam including an uplink service beam and a downlinkservice beam, each downlink service beam being associated with adifferent service beam coverage area which together form a combinedservice beam coverage area; first transmitting means for transmittingthe downlink service beams from the geosynchronous satellite, includingtransmitting at least one of the downlink service beams using a commondownlink frequency and a common downlink polarization; first receivingmeans for receiving the uplink service beams at the geosynchronoussatellite; means for establishing an uplink feeder beam and a downlinkfeeder beam between the geosynchronous satellite and a gateway, thedownlink feeder beam being associated with a feeder beam coverage areaat least partially not overlapping the combined service beam coveragearea; second receiving means for receiving the uplink feeder beam;means, coupled to the first transmitting means, for forming theplurality of downlink service beams from the uplink feeder beam; meansfor forming the downlink feeder beam from the plurality of uplinkservice beams; and second transmitting means, coupled to the means forforming the downlink feeder beam, for transmitting the downlink feederbeam using the common downlink frequency and the common downlinkpolarization.
 18. A geosynchronous satellite, comprising: a firstantenna for: establishing a plurality of composite service beams betweenthe geosynchronous satellite and a plurality of user terminals, eachcomposite service beam including an uplink service beam and a downlinkservice beam, each downlink service beam being associated with adifferent service beam coverage area which together form a combinedservice beam coverage area, transmitting the downlink service beams fromthe geosynchronous satellite, at least one of the downlink service beamstransmitted using a common downlink frequency and a common downlinkpolarization, and receiving the uplink service beams at thegeosynchronous satellite, a second antenna for: establishing an uplinkfeeder beam and a downlink feeder beam between the geosynchronoussatellite and a gateway, the downlink feeder beam being associated witha feeder beam coverage area at least partially not overlapping thecombined service beam coverage area, receiving the uplink feeder beam,and transmitting the downlink feeder beam using the common downlinkfrequency and the common downlink polarization; and a plurality offrequency translators coupled to the first and second antennas, for:forming the plurality of downlink service beams from the uplink feederbeam, forming the downlink feeder beam from the plurality of uplinkservice beams, and frequency translating the uplink feeder beam and oneor more of the plurality of uplink service beams.